Using new redox mediators/buffers and our electrical titration apparatus, we have been able to extend the range of potentiometric titrations up to 900 mV (vs. S.H.E.). With this new capability we have found a high voltage transition of heme a3 with an Em 780 mV. The reduced form of this high potential heme a3 cannot bind CO. Three essential conditions have been established for the formation of the unique "pulsed-like" low potential form of heme a3 with a Soret peak at 429 nm. In the absence of any of the 3 conditions, a different form of low potential heme a3 with a Soret at 448 nm is seen. Preliminary evidence indicates that the pulsed-like form is in a lipoprotein environment, and that it is this form which binds CO in both the oxidized and reduced states. In collaboration with the Johnson Foundation at the University of Pennsylvania, we have used SVD to analyze transient kinetic forms of cytochrome oxidase which arise during the oxidation of the reduced enzyme by 02. We find the same kinds of unique spectra and spectral transitions that we have seen in our equilibrium studies.